Expression of hepatic cholesterol 7α-hydroxylase (CYP7A1) is negatively regulated by orphan nuclear receptor small heterodimer partner (SHP). In this study, we aimed to find whether thyroid hormone regulates SHP expression by modulating the transcriptional activities of liver receptor homolog-1 (LRH-1).

We injected thyroid hormone (triiodothyronine, T3) to C57BL/6J wild type. RNA was isolated from mouse liver and used for microarray analysis and quantitative real-time polymerase chain reaction (PCR). Human hepatoma cell and primary hepatocytes from mouse liver were used to confirm the effect of T3 in vitro. Promoter assay and electrophoretic mobility-shift assay (EMSA) were also performed using human hepatoma cell line

Initial microarray results indicated that SHP expression is markedly decreased in livers of T3 treated mice. We confirmed that T3 repressed SHP expression in the liver of mice as well as in mouse primary hepatocytes and human hepatoma cells by real-time PCR analysis. LRH-1 increased the promoter activity of SHP; however, this increased activity was markedly decreased after thyroid hormone receptor β/retinoid X receptor α/T3 administration. EMSA revealed that T3 inhibits specific LRH-1 DNA binding.

We found that thyroid hormone regulates the expression of SHP mRNA through interference with the transcription factor, LRH-1.

Damaged mitochondria are removed by autophagy. Therefore, impairment of autophagy induces the accumulation of damaged mitochondria and mitochondrial dysfunction in most mammalian cells. Here, we investigated mitochondrial function and the expression of mitochondrial complexes in autophagy-related 7 (Atg7)-deficient β-cells.

To evaluate the effect of autophagy deficiency on mitochondrial function in pancreatic β-cells, we isolated islets from Atg7^F/F:RIP-Cre+ mice and wild-type littermates. Oxygen consumption rate and intracellular adenosine 5'-triphosphate (ATP) content were measured. The expression of mitochondrial complex genes in Atg7-deficient islets and in β-TC6 cells transfected with siAtg7 was measured by quantitative real-time polymerase chain reaction.

Baseline oxygen consumption rate of Atg7-deficient islets was significantly lower than that of control islets (P<0.05). Intracellular ATP content of Atg7-deficient islets during glucose stimulation was also significantly lower than that of control islets (P<0.05). By Oxygraph-2k analysis, mitochondrial respiration in Atg7-deficient islets was significantly decreased overall, although state 3 respiration and responses to antimycin A were unaffected. The mRNA levels of mitochondrial complexes I, II, III, and V in Atg7-deficient islets were significantly lower than in control islets (P<0.05). Down-regulation of Atg7 in β-TC6 cells also reduced the expression of complexes I and II, with marginal significance (P<0.1).

Impairment of autophagy in pancreatic β-cells suppressed the expression of some mitochondrial respiratory complexes, and may contribute to mitochondrial dysfunction. Among the complexes, I and II seem to be most vulnerable to autophagy deficiency.